The present invention relates to a transmission comprising a hydraulic coupling member and a locking or blocking clutch, and more particularly to a motor vehicle transmission of the kind comprising, between an input element which is intended to rotate integrally with a first shaft (generally a drive shaft), and an output element which is intended to rotate integrally with a second shaft (generally a driven shaft), firstly a hydraulic coupling member such as a torque converter, which comprises an impeller wheel rotating integrally with the input element, and a turbine wheel rotating integrally with the output element, and secondly, a locking or blocking clutch, commonly called a "LOCK UP," which, upon starting and generally upon each change of gear ratio is in a first, disengaged, condition in which the hydraulic coupling member alone operatively interconnects the input element and the output element, and which, in a second engaged condition, once the initial starting phase has been completed, renders this hydraulic coupling member inoperative and locks up the transmission so as to eliminate any residual slipping due to said member and so as to improve thereby the efficiency of the whole assembly, by ensuring a direct mechanical coupling between the input element and the output element.
The invention is aimed, more precisely at transmissions of this kind which are intended to be incorporated in motor vehicles.
These can be either transmissions with semi-automatic control or transmissions with fully automatic control.
In practice, in transmissions of this kind, the locking clutch possesses a coupling element which is mounted to be movable axially and which, rotating integrally with the output element, is capable of being made to rotate integrally with the input element by means of friction.
Likewise in practice, for transmissions of this kind, fluid-circulation means are provided which comprise an inlet pipe for supplying fluid under pressure and an outlet pipe for returning said fluid to a collecting tank.
In the prior art, the locking or blocking clutch usually is controlled by adjusting the direction of circulation of this fluid under pressure: in one direction of circulation, the fluid under pressure penetrates into the transmission via a control chamber engaged with or disengaged from the clutch, which is referred to below as the control chamber and which is formed between the coupling element of said clutch and a wall integral with the input element, so that this clutch is then maintained in a disengaged position; for the opposite direction of circulation, the fluid under pressure penetrates into the transmission via the hydraulic coupling member so that it presses the coupling element of the clutch against the said wall of the input element and so that the clutch is, in this way, adjusted to the engaged position.
In practice, the corresponding controls have always been arranged on the exterior of the transmission, on the fluid-circulation means which serve said transmission, and the result is that, to change from a transmission having no locking or blocking clutch to a transmission having such a clutch, it is necessary to substantially modify these fluid-circulation means. This can be difficult and troublesome to carry out, at least for certain applications.
Consequently, provision has been made in the present invention to integrate with the transmission itself, when it has a locking or blocking clutch, the means designed to bring this clutch into, or out of, operation.
In the known arrangement proposed for this purpose, there is provided on the transmission inlet pipe, within the transmission itself, a tubular distributor slide-valve, which, via its central bore, is suitable for permanently serving the hydraulic coupling member, and which, acted upon by elastic means restoring it in the direction of a position of rest, is movable between such a position of rest, in which it blocks a passage, referred to below as the control passage, which causes said inlet pipe to communicate with the control chamber of the clutch, and a working position, in which, by opening said control passage, it permits free communication between the inlet pipe and the control chamber of the clutch, to effect disengagement of said clutch. There are also provided on the outlet pipe of the transmission, on the exterior of this transmission, two passages which are arranged in parallel, each of which is regulated by a controlled clack-valve, said passages thus constituting together means of passage with a variable cross-section which is regulated by said controlled clack-valve.
When these two clack-valves are open the pressure at the outlet of the transmission is relatively low, so that, by means of the pressure at the inlet or the supply pressure, the distributor slide-valve is forced into the working position. This opens the control passage of the clutch and consequently, said clutch is adjusted into the disengaged position.
When the clack-valve which is controlled is closed the pressure at the outlet of the transmission is sufficient to ensure that, as the pressure difference at the inlet and at the outlet becomes less than the load of its elastic restoring means, the distributor slide-valve blocks the control passage of the clutch. The said clutch is then no longer set in the disengaged position and can normally, subject to the then relatively elevated pressure which prevails in the transmission, pass into the engaged position.
Nevertheless, in practice, when the valve is in the position of rest, such an arrangement can fail due to the fact that, since one and the same pressure then prevails on both faces of the coupling element of the clutch, this coupling element is not applied sufficiently energetically to the corresponding wall of the input element.
An object of the present invention is to provide an arrangement which enables this disadvantage to be minimised or avoided.